Device for measuring interpupilary distance.



,0. M. STEVENSON. v DEVICE FOR MEASURING INTERPUPILARY DISTANCE.

APPLICATION FILED MAR. 2, 1911.

1,01%,917. Patented Jan. 16,1912.

FFTC

CLARENCE M. STEVENSON, OF LOS ANGELES, CALIFORNIA.

DEVICE FOR MEASURING INTERPUPILARY DISTANCE.

Specification of Letters Patent.

Application filed March 2, 1911. Serial No. 611,893.

To all whom it may concern:

Be it known that I, CLARENCE M. STEVEN- son, a citizen of the United States, residing at Los Angeles, in the county of Los Angeles and State of California, have invented a ne and useful Device for Measuring Interpup'ilary Distance, of which the following is a specification.

This invention relates to means for measuring the distance between the pupils of the eyes of a person in order to facilitate the accurate fitting of eye-glasses or spectacles. 1

One object of the invention is to provide means whereby the 'interpupilary distance may be measured accurately and conveniently.

Another object of the invention is to pro Vide a device for this purpose in which the distance may be measured correctly when the eyes are in the position for which the. glasses are adapted, so as to take account of the approximation of the pupils for a short distance focus, as in reading-glasses.

Other objects of the invention will appear hereinafter. 1

The accompanying drawings illustrate the invention, and referring thereto:

Figure 1 is a perspective of the device with parts broken away. Fig. 2 is a plan thereof. Fig. 3 is a vertical section on line as -m Fig. 2.. Fig. 4% is a transverse sec tion on line a2*-m in Fig. 3. Fig. 5 is a l' ori'zontal section on line 00 4; in Fig. '1'. Fig. (Sis a perspective of a target servingas means for fixing the position ofthe patients eyes.

1 designates a stand or base for supportingthe instrument, the base being provided with a post 2 in which telescopes a vertical bar- 3 which may be clamped at any desired elevation in said post by a set screw 4-, said bar 3 carrying at its upper end a head on which is mounted a horizontal bar or member 6 serving as a scale member for the instrument. At one end of this bar 6 is provided a head rest or means for engagement with a part of the face of a person, for example, the forehead, said means consisting of a cross bar 7 mounted on a bar 8 extending upwardly from the horizontal bar 6. The said bar 6 is tubular or provided with a longitudinal bore in which slides a horizontal slide member 9 provided on the end opposite to the'arin 8 with anupwardly expassing through the axis of the perforations 13 and 1-1. Stud shdc member 9 is further provided with an upwardly extending lug or projection 15 engaging and sliding in a longitudinal slot 16 in the horizontal memher 6, this-projection being provided with a mark 17 adapted to read on scales 18, 19 on the'member 6 at the respective sides of'the slot 16. The member 9 is moved longitudinally within the tubular niemberti by means of a manual operating device, such as a thumb wheel 20 carried by a shaft 21 rotatably mounted in bearings on the member 6, said'shaft carrying a gear wheel 23 engaging with a rack 24 on the member 9. Said member 6 may also be provided with a thumb wheel 25 screwing on shaft 21 and engaging wit-hone of the bearings 22-to clamp the parts in set position.

Means are prefe'ably provided for illuminating the eyes to be observed, said means consisting, for example, of electric lamps 27 contained in reflector cases 28 supported on arm 29 on the head 5, said cases being provided with translucent front plates 30 and said lamps being connected tov electric supply wires 31 leading to a connecting plug 32 for connection to any suitable source. of current. Means are also preferably provided for bringing the eyes to a definitevconver gence or focal distance, said means consisting, for example, of a mirror 31 slidably mounted on a longitudinal bar extending above the bar 6, said bar being, for example, secured to the bar 8 at one end and to arms 36 at the other end, said arms extending from the lamp cases 28 aforesaid. A target 37 is provided on the back of head rest 7 having a center mark or -depression 37.

The operation is as".follows: A person whose.interpupilary distance is to be meas ured, places his forehead against the bar 7,

Patented Jan. 16,1912. I

4 are, however,

.mirror placed at six and one-half inches from thebar 7. Said person looks at the image in the mirror of the center mark 37, thereby bringing his eyes to the same convergence as if he were looking at an actual object at the distancefor which the glasses are to be fitted. The observer places his eye in the position indicated at c in Fig. 2,

' and looking through the double prism 11- observes the apparent position, say of the inner edges of the pupils, at a. On account of the refraction bythe double prism the rays, dicated at a, c, from a to the eye at 0, will be deflected as indicated at a, a, so as to become more nearly parallel or less convergent, so that the observer sees visual images, of a, b at b, and the distance H'fis proportional to the distance a-c between the observerseye and the eyes being observed. The images referred to are those produced by the rays of light passing from each of the, patients eyes through the prism at the other side of the center, such rays'being refracted toward the center of the double prism and giving the effect, therefore, of an image which is deflected inwardly from tln object. In addition to these virtual images which are closer together than the object observed, other images are .produced which are farther apart than said objects, these outer images being due to the refraction of the rays from each eye which pass through the portion of the prism at the same side. These outer images disregarded in reading the apparatus, only the inner images being observed. The observer now moves the eyepiece and double prism forward or back by means of the manual operating device 20 until the inner edges of the pupils for the two visual images coincide, this position of the visual images, indicated at a b being, therefore, on the longitudinal axis or central line a c of the instrument. If 0 be the adjusted position of the observers eye at this time, it being understood that the observer moves his eye so as to follow up the double prism in its change of position, then the'distan'ce from 0 to c is dependent on the linear distance (z-'03. Therefore, by calculation or observation,'-a scale maybe formed on the fixed member 6 whose readings on the movable member 16 will indicate the distance arr-a or preferably twice that distancewhich is the interpupilary distance. Such a scale, for example, is indicated at 18.

It will be understood that the scale 18 is laid out to represent the interpupilary distances corresponding to the longitudinal tion of the slide member, but represents member connected thereto,

movement of the eyepiece with relation to the head rest or means for fixing the location of the patients eyes, and the scale 18 therefore does not represent the actual mothe motion multiplied by a certain factor pendent on the angle of deflection by double prism and also to some extent on the convergence of ,the patients eyes as determined by the target 37 and mirror. The scale 18 may thus be laid off to'represent the interpupilary distance'for the standard or normal position of the eyes in reading,.

the mirror being adjusted to that position. The, other scale 19 on the scale member may be laid OH to represent the interpupilary distances for distance-glasses, where the eyes are looking at a distant object. sired, the scale 18 may be laid off as an actual scale in centimeters, for example, and the actual interpupilary distance corresponding thereto maybe determined by suitable charts, tables or formulae.

The above described movable mirror, in connection with the supporting scale member therefor and the indicator or target 37,.may also be used for other purposes, for example,

in ascertaining the power of convergence or accommodation. of the eyes to a given focus, the mirror being moved to diiferent positions and the patient being instructed to look at the indicator or target 87 with both eyes and the observer or examiner noting the point at which the power of concentrating both eyes on the same point ceases.

WVhat I claim is:

1. A device for measuring interpupilary distance comprising means for fixing the location of the eyes to be measured, an eyepiece movably relatively to the aforesaid means, and scale means for measuring the movement of said eye-piece relatively to the aforesaid means, said eye-piece being provided with ray deflecting means for producing virtual images of the observed eyes this Or, if dewhen viewed from the eye-piece, said virrest, a double pr1sm,means for movably mounting said double prism relatively to said head rest, and a scale means for indicating the relative movement of said double prism and head rest.

1. A device for measuring interpupilary distance comprising ahead rest, a scale a slide member.

mounted to move longitudinally on said scale member, and an eye piece on said slide member provided with a double prism.

5. The combination of a head rest, an indicator thereon, a scale member extending from said head'rest, and a mirror movably' mounted on, said scale member and facing said indicator, whereby the eyes of a person located by said-head rest may be positioned to definite focal distance by observa tion of said indicator in said mirror. 1

6. A device for measuring interpupilary distance comprising a head rest, a scale member connected thereto, a slide member mounted to move. longitudinally on 'said scale member, an eye piece on said slide member provided with a double prism, and illuminating means supported in position to direct light toward the head rest.

7. A device for determining the distance between pupils of a person comprising a head rest, a double prism, means for movprism and head rest, and a mirror mounted to move on said scale means.

In testimony whereof, I have hereunto set my hand at -Los Angeles, California, this 11th day of February, 1911.

CLARENCE M. STEVENSON.

In presencev of ARTHUR P. KNIGHT, FRANK L. A. GRAHAM. 

